GPS Civil Interface Observations

1
GPS Civil Interface Observations

• Rick Hamilton
• CGSIC Executive Secretariat
• U.S. Coast Guard Navigation Center

2
ICD Compliance Issues

• Provide non-attribution forum to
• Inform the users community of recent past issues
• Ensure correct balance btwn transparency OPSEC
• Seek feedback regarding clarification of
  IS-GPS-200
• Prevent future GPS receiver problems

3
Scenario 1 Af0 value indicates satellite clock
instability

• Issue - User thought zero value for Af0 Subframe
  4-5 could be used to indicate satellite clock
  instability and excluded satellite from solution
  regardless of satellites actual health setting.
• Affected Data - Bits 271278 290292 of
  satellite-specific pages.
• Resolution Zero value does not indicate
  instability in satellite clock and should not be
  used to determine satellite integrity.
• There are a variety of constellation maintenance
  activities that could result in a zero value for
  a satellite that is still set HEALTHY and meeting
  all specification requirements.
• IS-GPS-200E, ..occasional CS actions to manage
  clock offsets may also inhibit the ability to
  provide specified almanac time parameter
  accuracies.

4
Scenario 2 Using almanac data from unhealthy
satellites

• Issue - User attempted to use subframe 4-5
  almanac data from satellites set to UNHEALTHY.
• Affected Data All broadcast navigation data.
• Resolution
• Sections 20.3.3.3.1.4 and 20.3.3.5.1.3 of
  IS-GPS-200E define the health indicators
  broadcast by the constellation.
• These indicators are used to warn users when
  "some or all NAV data are bad" for a specific
  satellite due to an on-orbit anomaly or
  maintenance activity.
• Use of any portion of the navigation and timing
  signal from asatellite set to any status other
  than "HEALTHY is at the user's own risk.

5
Scenario 3 Restricting possible WNa/toa
combinations

• Issue User reasoned that there would not be
  more than two WNa/toa combinations seen at any
  one time (previous day and current day).
• Affected Data Bits 69-84 of Subframe 5 Page 25
  and Bits 91-98 in satellite specific pages of
  Subframes 4 and 5.
• Resolution
• There are no restrictions in IS-GPS-200E that
  limit the CS to only two combinations. Section
  20.3.3.5.2.2 states Within each upload, the CS
  shall ensure that all toa values in subframes 4
  and 5 shall be the same for a given almanac data
  set and shall differ for successive data sets
  which contain changes in almanac parameters or SV
  health.
• Opportunity to clarify the standard?

6
User Comments

• Comments received at the 2009 CGSIC meeting
• There was a General NANU sent that predicted a
  high HDOP, no event was experienced, and no
  further explanation or follow-up was received.
• Some satellites were taken out of service until
  further notice by a UNUSUFN NANU and another
  with a GENERAL NANU.
• There has been a higher than normal amount of
  NANU errors recently.

7
User Comments
User Comments

• Comments received at the 2009 CGSIC meeting
• NANUs should be automated and automatically
  generated to keep humans out of the process.
• Users would like to see NANUs delivered in
  plain language text.
• RAIM predictions are typically calculated for 72
  hours into the future, our systems therefore rely
  on the availability of the latest constellation
  updates as they can impact the current prediction
  scenario period.
• Manual intervention was required to generate a
  system-parsable outage type

8
User Comments
User Comments

• User conclusions
• Standardization of event reporting required
• Use computer readable fixed formats
• Leave general free text for information
• Lets help one another to interpret NANUs for the
  user

9
Response Actions
Response Actions

• Improvements initiated by 2SOPS
• Increased quality control standardization (new
  NANU types)
• Improvements to operational transparency with
  increased NANU transmissions and improved text
  dialog
• ICD-GPS-240 Updated
• ICD-GPS-870, OCX User Interface
• Interface Control Working Group meetings
• Address current issues
• Update as required
• Approved for public coordination
• Solicit User Input
• ICD-GPS-870 Public Interface Control Working
  Group
• NAVCEN Website
• Information Dissemination Coordination Team
• Being Chartered under the National Space-Based
  PNT Executive Committee

10
IS-GPS-200 Clarification Feedback
http//www.navcen.uscg.gov/
Rick Hamilton CGSIC Executive Secretariat USCG
Navigation Center Rick.Hamilton_at_uscg.mil
11
NANU Template/Examples
FCSTDV TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
FORECAST OUTAGE JDAY JJJ/HHMM - JDAY JJJ/HHMM 1.
NANU TYPE FCSTDV NANU NUMBER YYYYSSS NANU
DTG DDHHMMZ MMM YYYY REFERENCE NANU N/A REF
NANU DTG N/A SVN XX PRN XX START JDAY
JJJ START TIME ZULU HHMM START CALENDAR
DATE DD MMM YYYY STOP JDAY JJJ STOP TIME
ZULU HHMM STOP CALENDAR DATE DD MMM YYYY 2.
CONDITION GPS SATELLITE SVNXX (PRNXX) WILL BE
UNUSABLE ON JDAY JJJ (DD MMM YYYY) BEGINNING
HHMM ZULU UNTIL JDAY JJJ (DD MMM YYYY) ENDING
HHMM ZULU. 3. POC CIVILIAN - NAVCEN AT
703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
12
NANU Template/Examples
FCSTMX TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
FORECAST OUTAGE JDAY JJJ/HHMM - JDAY JJJ/HHMM 1.
NANU TYPE FCSTMX NANU NUMBER YYYYSSS NANU
DTG DDHHMMZ MMM YYYY REFERENCE NANU N/A REF
NANU DTG N/A SVN XX PRN XX START JDAY
JJJ START TIME ZULU HHMM START CALENDAR
DATE DD MMM YYYY STOP JDAY JJJ STOP TIME
ZULU HHMM STOP CALENDAR DATE DD MMM YYYY 2.
CONDITION GPS SATELLITE SVNXX (PRNXX) WILL BE
UNUSABLE ON JDAY JJJ (DD MMM YYYY) BEGINNING
HHMM ZULU UNTIL JDAY JJJ (DD MMM YYYY) ENDING
HHMM ZULU. 3. POC CIVILIAN - NAVCEN AT
703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
13
NANU Template/Examples
FCSTEXTD TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
FORECAST OUTAGE EXTENDED UNTIL FURTHER NOTICE 1.
NANU TYPE FCSTEXTD NANU NUMBER YYYYSSS NANU
DTG DDHHMMZ MMM YYYY REFERENCE NANU YYYYNNN
REF NANU DTG DDHHMMZ MMM YYYY SVN XX PRN
XX START JDAY JJJ START TIME ZULU HHMM
START CALENDAR DATE DD MMM YYYY STOP JDAY
UFN STOP TIME ZULU N/A STOP CALENDAR DATE
N/A 2. CONDITION THE FORECAST OUTAGE FOR GPS
SATELLITE SVNXX (PRNXX) IS EXTENDED UNTIL FURTHER
NOTICE. 3. POC CIVILIAN - NAVCEN AT
703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
14
NANU Template/Examples
FCSTSUMM TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
FORECAST OUTAGE SUMMARY JDAY JJJ/HHMM - JDAY
JJJ/HHMM 1. NANU TYPE FCSTSUMM NANU NUMBER
YYYYSSS NANU DTG DDHHMMZ MMM YYYY REFERENCE
NANU YYYYNNN REF NANU DTG DDHHMMZ MMM YYYY
SVN XX PRN XX START JDAY JJJ START
TIME ZULU HHMM START CALENDAR DATE DD MMM
YYYY STOP JDAY JJJ STOP TIME ZULU HHMM
STOP CALENDAR DATE DD MMM YYYY 2. CONDITION
GPS SATELLITE SVNXX (PRNXX) WAS UNUSABLE ON JDAY
JJJ (DD MMM YYYY) BEGINNING HHMM ZULU UNTIL JDAY
JJJ (DD MMM YYYY) ENDING HHMM ZULU. 3. POC
CIVILIAN - NAVCEN AT 703-313-5900,
HTTP//WWW.NAVCEN.USCG.GOV MILITARY - GPS
Support Center at HTTP//WWW.SCHRIEVER.AF.MIL/GPSS
UPPORTCENTER, DSN 560-2541, COMM 719-567-2493,
GPS_at_SCHRIEVER.AF.MIL, HTTP//WWW.SCHRIEVER.AF.MIL/
GPS MILITARY ALTERNATE - 14 AF AIR SPACE
OPERATIONS CENTER, DSN 276-9994.COMM
805-606-9994. V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
15
NANU Template/Examples
FCSTCANC TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVN13 (PRN02)
FORECAST OUTAGE CANCELLED 1. NANU TYPE FCSTCANC
NANU NUMBER YYYYSSS NANU DTG DDHHMMZ MMM
YYYY REFERENCE NANU YYYYNNN REF NANU DTG
DDHHMMZ MMM YYYY SVN XX PRN XX START
JDAY JJJ START TIME ZULU HHMM START
CALENDAR DATE DD MMM YYYY STOP JDAY CANCELLED
STOP TIME ZULU N/A STOP CALENDAR DATE N/A
2. CONDITION THE FORECAST OUTAGE FOR GPS
SATELLITE SVNXX (PRNXX) SCHEDULED FOR JDAY JJJ
(DD MMM YYYY) BEGINNING HHMM ZULU HAS BEEN
CANCELLED. 3. POC CIVILIAN - NAVCEN AT
703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
16
NANU Template/Examples
FCSTRESCD TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
FORECAST OUTAGE RESCHEDULED 1. NANU TYPE
FCSTRESCD NANU NUMBER YYYYSSS NANU DTG
DDHHMMZ MMM YYYY REFERENCE NANU YYYYNNN REF
NANU DTG DDHHMMZ MMM YYYY SVN XX PRN XX
START JDAY JJJ START TIME ZULU HHMM START
CALENDAR DATE DD MMM YYYY STOP JDAY JJJ
STOP TIME ZULU HHMM STOP CALENDAR DATE DD
MMM YYYY 2. CONDITION GPS SATELLITE SVNXX
(PRNXX) WILL BE UNUSABLE ON JDAY JJJ (DD MMM
YYYY) BEGINNING HHMM ZULU UNTIL JDAY JJJ (DD MMM
YYYY) ENDING HHMM ZULU. PLEASE REFERENCE NANU
NUMBER YYYYNNN DTG DDHHMMZ MMM YYYY FOR THE
ORIGINAL OUTAGE TIME. 3. POC CIVILIAN - NAVCEN
AT 703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
17
NANU Template/Examples
UNUSUFN TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
UNUSABLE JDAY JJJ/HHMM - UNTIL FURTHER NOTICE 1.
NANU TYPE UNUSUFN NANU NUMBER YYYYSSS NANU
DTG DDHHMMZ MMM YYYY REFERENCE NANU N/A REF
NANU DTG N/A SVN XX PRN XX START JDAY
JJJ START TIME ZULU HHMM START CALENDAR
DATE DD MMM YYYY STOP JDAY UFN STOP TIME
ZULU N/A STOP CALENDAR DATE N/A 2.
CONDITION GPS SATELLITE SVNXX (PRNXX) WILL BE
UNUSABLE ON JDAY JJJ (DD MMM YYYY) BEGINNING
HHMM ZULU UNTIL FURTHER NOTICE. 3. POC CIVILIAN
- NAVCEN AT 703-313-5900, HTTP//WWW.NAVCEN.USCG.G
OV MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
18
NANU Template/Examples
UNUSABLE TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
UNUSABLE JDAY JJJ/HHMM - JDAY JJJ/HHMM 1. NANU
TYPE UNUSABLE NANU NUMBER YYYYSSS NANU DTG
DDHHMMZ MMM YYYY REFERENCE NANU YYYYNNN REF
NANU DTG DDHHMMZ MMM YYYY SVN XX PRN XX
START JDAY JJJ START TIME ZULU HHMM START
CALENDAR DATE DD MMM YYYY STOP JDAY JJJ
STOP TIME ZULU HHMM STOP CALENDAR DATE DD
MMM YYYY 2. CONDITION GPS SATELLITE SVNXX
(PRNXX) WAS UNUSABLE ON JDAY JJJ (DD MMM YYYY)
BEGINNING HHMM ZULU UNTIL JDAY JJJ (DD MMM YYYY)
ENDING HHMM ZULU. 3. POC CIVILIAN - NAVCEN AT
703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
19
NANU Template/Examples
UNUNOREF TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX)
UNUSABLE JDAY JJJ/HHMM - JDAY JJJ/HHMM 1. NANU
TYPE UNUNOREF NANU NUMBER YYYYSSS NANU DTG
DDHHMMZ MMM YYYY REFERENCE NANU N/A REF NANU
DTG N/A SVN XX PRN XX START JDAY JJJ
START TIME ZULU HHMM START CALENDAR DATE DD
MMM YYYY STOP JDAY JJJ STOP TIME ZULU HHMM
STOP CALENDAR DATE DD MMM YYYY 2. CONDITION
GPS SATELLITE SVNXX (PRNXX) WAS UNUSABLE ON JDAY
JJJ (DD MMM YYYY) BEGINNING HHMM ZULU UNTIL JDAY
JJJ (DD MMM YYYY) ENDING HHMM ZULU. 3. POC
CIVILIAN - NAVCEN AT 703-313-5900,
HTTP//WWW.NAVCEN.USCG.GOV MILITARY - GPS
Support Center at HTTP//WWW.SCHRIEVER.AF.MIL/GPSS
UPPORTCENTER, DSN 560-2541, COMM 719-567-2493,
GPS_at_SCHRIEVER.AF.MIL, HTTP//WWW.SCHRIEVER.AF.MIL/
GPS MILITARY ALTERNATE - 14 AF AIR SPACE
OPERATIONS CENTER, DSN 276-9994.COMM
805-606-9994. V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
20
NANU Template/Examples
USABINIT TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ SVNXX (PRNXX) USABLE
JDAY JJJ/HHMM 1. NANU TYPE USABINIT NANU
NUMBER YYYYSSS NANU DTG DDHHMMZ MMM YYYY
REFERENCE NANU N/A REF NANU DTG N/A SVN
XX PRN XX START JDAY JJJ START TIME ZULU
HHMM START CALENDAR DATE DD MMM YYYY STOP
JDAY N/A STOP TIME ZULU N/A STOP CALENDAR
DATE N/A 2. CONDITION GPS SATELLITE SVNXX
(PRNXX) WAS USABLE AS OF JDAY JJJ (DD MMM YYYY)
BEGINNING HHMM ZULU. 3. POC CIVILIAN - NAVCEN
AT 703-313-5900, HTTP//WWW.NAVCEN.USCG.GOV
MILITARY - GPS Support Center at
HTTP//WWW.SCHRIEVER.AF.MIL/GPSSUPPORTCENTER, DSN
560-2541, COMM 719-567-2493, GPS_at_SCHRIEVER.AF.MIL
, HTTP//WWW.SCHRIEVER.AF.MIL/GPS MILITARY
ALTERNATE - 14 AF AIR SPACE OPERATIONS CENTER,
DSN 276-9994.COMM 805-606-9994.
V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
21
NANU Template/Examples
LEAPSEC TEMPLATE NOTICE ADVISORY TO NAVSTAR
USERS (NANU) YYYYSSS SUBJ LEAP SECOND 1.
CONDITION THE INTERNATIONAL EARTH ROTATION
SERVICE (IERS) HAS ANNOUNCED THE INTRODUCTION OF
A LEAP SECOND TO OCCUR AT THE END OF MMM YYYY
2. COORDINATED UNIVERSAL TIME (UTC) WILL
SEQUENCE AS FOLLOWS DD MMM YYYY HH HOURS MM
MINUTES SS SECONDS DD MMM YYYY HH HOURS MM
MINUTES SS SECONDS DD MMM YYYY HH HOURS MM
MINUTES SS SECONDS 3. FOR GPS, AS WITH PREVIOUS
LEAP SECOND UPDATES, THE UTC DATA IN SUBFRAME
4,PAGE 18 OF THE NAVIGATION MESSAGE WILL CHANGE
IN ACCORDANCE WITH ICD-GPS-200. BEFORE THE LEAP
SECOND GPS-UTC IS XX (GPS IS AHEAD OF UTC BY XX
SECONDS) AFTER THE LEAP SECOND GPS-UTC WILL BE
XX (GPS WILL BE AHEAD OF UTC BY XX SECONDS) 4.
POC CIVILIAN - NAVCEN AT 703-313-5900,
HTTP//WWW.NAVCEN.USCG.GOV MILITARY - GPS
Support Center at HTTP//WWW.SCHRIEVER.AF.MIL/GPSS
UPPORTCENTER, DSN 560-2541, COMM 719-567-2493,
GPS_at_SCHRIEVER.AF.MIL, HTTP//WWW.SCHRIEVER.AF.MIL/
GPS MILITARY ALTERNATE - 14 AF AIR SPACE
OPERATIONS CENTER, DSN 276-9994.COMM
805-606-9994. V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
22
NANU Template/Examples
LAUNCH TEMPLATE 1. NANU TYPE LAUNCH
GENERAL MESSAGE TO ALL GPS USERS 2. GPS
SATELLITE SVNXX (PRNXX) WAS LAUNCHED ON JDAY JJJ
(DD MMM YYYY). A USABINIT NANU WILL BE SENT WHEN
THE SATELLITE IS SET ACTIVE TO SERVICE. 3. POC
CIVILIAN - NAVCEN AT 703-313-5900,
HTTP//WWW.NAVCEN.USCG.GOV MILITARY - GPS
Support Center at HTTP//WWW.SCHRIEVER.AF.MIL/GPSS
UPPORTCENTER, DSN 560-2541, COMM 719-567-2493,
GPS_at_SCHRIEVER.AF.MIL, HTTP//WWW.SCHRIEVER.AF.MIL/
GPS MILITARY ALTERNATE - 14 AF AIR SPACE
OPERATIONS CENTER, DSN 276-9994.COMM
805-606-9994. V3SPACEAF.AOC_at_VANDENBERG.AF.MIL
GENERAL MESSAGE TO ALL GPS USERS